Hair usually begins to gray in middle adulthood because of ______.

A) a decrease in the production of melanin
B) the replacement of muscle tissues by fat tissues
C) an increase in the production of insulin
D) a decrease in the production of prolactin

Melanin

A pigment that gives color to the skin, hair, and eyes, and plays a crucial role in protecting the skin against UV radiation.

Insulin

A hormone produced by the pancreas that regulates blood sugar levels by facilitating the uptake of glucose into tissues.

Prolactin

A hormone produced by the pituitary gland that stimulates milk production after childbirth and affects sex hormone levels.